1. Field of the Invention
The present invention relates to recording/playback devices and, more specifically, to a recording/playback device having a function of simultaneously recording and reproducing television broadcast signals and audio broadcast signals.
2. Description of the Background Art
Conventionally, recording/playback devices for simultaneously recording and playing back television broadcast streams or audio broadcast streams have utilized either one or both of two types of program playback schemes: chasing playback and catching-up playback. Chasing playback simply allows simultaneous recording and playback. For example, when a user gets back home in the course of preprogrammed recording and desires to watch the program being recorded, the program is played back from the beginning at single speed without a wait for the end of recording but with recording being continued. On the other hand, catching-up playback allows fast-forward playback of a program at a speed higher than single speed with recording being continued. With this, a missed portion of the program can be quickly viewed and then, eventually, a portion currently being broadcasted can be caught up with. An example of such catching-up playback is achieved by a recording/playback device disclosed in Japanese Patent Laid-Open Publication No. 2001-119671, wherein fast-forward playback is performed at a constant “1.5 times speed with natural voice” with voice pitch not being varied. With this, speech can be easy to listen even at the time of fast-forward playback, and therefore speech information will not be missed at the time of catching-up playback.
The structure of a conventional recording/playback device adopting such a scheme as mentioned above is described below with reference to FIGS. 10 through 13.
FIG. 10 is a functional block diagram showing the conventional recording/playback device. In FIG. 10, the conventional recording/playback device includes a simultaneous recording/reading unit 1, a playback speed changing unit 15, and an output switching unit 4. The simultaneous recording/reading unit 1 simultaneously records an input signal in a storage device and reads a signal recorded in the storage device, and detects a delay time of a signal read from the storage device (hereinafter simply referred to a read signal) with respect to the input signal. The playback speed changing unit 15 changes a playback speed of the read signal. The output switching unit 4 selects either one of the input signal and the read signal for output. At the start of catching-up playback, the output switching unit 4 outputs the read signal. When the delay time detected by the simultaneous recording/reading unit 1 is below a predetermined time, that is, immediately before played-back images catch up with real-time live broadcast, the output switching unit 4 switches its output from the read signal to the input signal.
FIG. 11 is a block diagram illustrating the structure of the simultaneous recording/reading unit 1. In FIG. 11, the simultaneous recording/reading unit 1 includes a data recording section 5, the storage device 6, a data reading section 7, and a time difference detecting section 8.
The data recording section 5 records an input signal in the storage device 6. The data recording section 5 may have incorporated therein an A/D converter for digitizing an analog signal or an encoder for encoding a digital signal. The encoder includes, for example, a video encoder and an audio encoder. The video encoder is an encoding means complying with moving picture compression standards, such as MPEG1, MPEG2, MPEG4, or Windows(R) Media Video (WMV). The audio encoder is an encoding means complying with audio compression standards, such as Dolby(R) AC3, dts, MPEG1-Layer II, MPEG2-AAC, MLP, or MPEG1-Layer III (MP3). Also, in order to achieve simultaneous recording and playback, a time for recording in the storage device 6 and a time for reading from the storage device 6 may be separated from each other for alternately perform recording and playback. In this case, the data recording section 5 is generally provided with a buffer memory for temporarily recording moving pictures and sounds.
The storage device 6 is a storage medium for digital signals and has a recording capacity sufficient for storing signal data for several tens of hours. For example, as the storage device 6, a hard disk drive, DVD-RAM, DVD-RW, DVD+RW, or a Blu-ray Disc can be used.
The data reading section 7 reads the data recorded by the data recording section 5 in the storage device 6 for output as the read signal. The data reading section 7 is generally provided with a buffer memory for temporarily recording moving pictures and sounds. This makes it possible in simultaneous recording and playback to achieve a process of alternately performing recording and playback by separating the time for recording in the storage device 6 and the time for reading from the storage device 6 from each other. The data reading section 7 can have incorporated therein a decoder for decoding a digital signal. The decoder includes, for example, a video decoder and an audio decoder. The video decoder is a decoding means complying with moving picture compression standards, such as MPEG1, MPEG2, MPEG4, or Windows(R) Media Video (WMV). The audio decoder is a decoding means complying with audio compression standards, such as The audio encoder is an encoding means complying with audio compression standards, such as Dolby(R) AC3, dts, MPEG1-Layer II, MPEG2-AAC, MLP, or MPEG1-Layer III (MP3).
The time difference detecting section 8 detects a difference in the time domain between a signal handled by the data recording section 5 and a signal handled by the data reading section 7. During catching-up playback, the time difference detecting section 8 compares a time stamp of the signal being recorded by the data recoding section 5 and a time stamp of the signal being read by the data reading section 7, and then detects their time difference.
Referring back to FIG. 10, the playback speed changing unit 15 includes a motion picture playback speed changing section and an audio playback speed changing section, both of which are not shown. The motion picture playback speed changing section changes a motion picture playback speed by using a playback scheme, such as, under MPEG standards, a playback scheme of skipping P pictures and B pictures or a playback scheme of skipping only B pictures. The audio playback speed changing section changes an audio playback speed by using the Pointer Interval Controlled OverLap and Add (PICOLA), in which decimation and insertion of a repetitive time waveform portion is performed to achieve compression and expansion of time-domain data, the OLA, in which cross fading of adjacent pieces of frame data is performed at predetermined time intervals to achieve compression and expansion of time-domain data, or the SOLA, in which a correlation between adjacent pieces of frame data is calculated and then the cross fading of a portion having the closest correlation is performed to achieve compression and expansion with high sound quality. Here, when the user selects catching-up playback through operation of a built-in button of the device or a remote controller, the playback speed changing unit 15 performs fast-forward playback. When fast-forward playback catches up with real time live broadcast currently being recorded, the playback speed changing unit 15 stops the speed changing process. At the same time, the simultaneous recording/reading unit 1 (the time difference detecting section 8) reports to the output switching unit 1 that catching-up playback has caught up with real time live broadcast. Upon reception of the report, the output switching unit 4 instantly switches the output to real time live broadcast.
As such, by combining a simultaneous recording/playback process and a playback speed changing process, a catching-up playback function can be achieved such that, for example, after a predetermined time has elapsed from the start of recording a program being broadcasted, the program is played back from the beginning at a 1.5 times speed while the recording continues, and then playback eventually catches up with real time live broadcast. FIG. 12 depicts an output (read signal or input signal) from the output switching unit 4. In FIG. 12, the horizontal axis represents a real time, whilst the vertical axis represents a broadcast time. FIG. 12 depicts an exemplary case where a real time live broadcast program (a two-hour program is assumed herein) is started to be broadcasted and recorded simultaneously and, when 20 minutes elapse from the start, catching-up playback (fast-forward playback at an approximately 1.4 times speed) is started. For example, when 50 minutes elapse from the start of recording, broadcast contents at a time after 40 minutes from the start of broadcasting the program are output. When 55 minutes elapse from the start of catching-up playback (that is, after 75 minutes from the start of recording), catching-up playback catches up with real time live broadcast. At this time, the output from the output switching unit 4 is switched from the read signal (catching-up playback) to the input signal (real time live broadcast).
However, the above-described conventional recording/playback device has the following problems. In the conventional recording/playback device, when catching-up playback catches up with real time live broadcast, simultaneous recording/playback is instantly switched to real time live broadcast. Whilst the recording process requires a procedure including a series of processes of encoding an input signal, recording the encoded signal in the storage device, reading the recorded signal from the recording device, and then decoding the read signal, real time live broadcast does not require such procedure. Therefore, a time lag always occurs between the input signal and the read signal. Therefore, dropout of sound information occurs at an instant when a switch is made to real time live broadcast. Moreover, the user cannot control over a switching timing. Therefore, when a switch is made while an actor is speaking his lines, for example, these lines cannot be completely output, thereby making the user feel uncomfortable. FIG. 13 depicts a state where dropout of sound information at a switching timing (at the time of around 75 minutes from the start of the program) occurs. In FIG. 13, when the time lag is one second, for example, the conventional recording/playback device determines that catching-up playback catches up with real time live broadcast when outputting broadcast contents at the time of 75 minutes sharp from the start of the program, and then switches the output. Consequently, sound information between 75 minutes sharp to 75 minutes and one second is not played back and therefore is dropped.